The present invention relates to a pneumatic control valve and circuit for supplying air pressure to a pneumatic cylinder in a truck transmission.
Transmissions for large over-the-road trucks frequently have 12 to 16 different gear ratios. In such transmissions, a pneumatic cylinder called a "range cylinder" is frequently used to move a rack to change the transmission from a low range of gear ratios to a high range of gear ratios. The rack is designed to be moved only when the transmission is in the neutral position, and a pneumatic control valve is provided to prevent movement of the range cylinder and rack when the transmission is not in the neutral position. Prior to applicant's invention, this pneumatic control valve was a spool valve of the type shown in U.S. Pat. No. 26,245, wherein movement of the spool valve is prevented by a mechanical transmission pin when the transmission is not in the neutral position.